Add per-signal requests counter.

[kovrus]

Add per signal request counter. See https://github.com/grafana/otel-squad/issues/11

We will have the following metrics:

• otlp_gateway_gcom_api_logs_requests_total
• otlp_gateway_gcom_api_metrics_requests_total
• otlp_gateway_gcom_api_traces_requests_total

with the following labels:

• org_id
• tenant_id
• cluster_url

It is similar to what OTLP gateway v1 exposes now. Additionally, OTLP gateway v1 exposes unknown cluster metrics, which would have to be replaced later by similar metrics in the routing processor.

Note:

The collector must be run with --feature-gates telemetry.useOtelForInternalMetrics to have these metrics exposed.